The present invention relates to a method and apparatus for evaluating luminous efficiency, sometimes referred to as relative quantum yield, which is applied for evaluating quality such as distribution of defects in a semiconductor substrate for, e.g., GaAs light-emitting diodes.
The quality evaluation of the luminous efficiency of, for example, a material substrate for GaAs light-emitting diodes (LEDs) is indispensable for the improvement of the luminous efficiency and the production yield of the LEDs. For laser diodes, the same is also necessary for the reduction and uniformity of their oscillation threshold.
Conventionally, test diodes that are formed from part of a substrate are used for the luminous efficiency evaluation. To determine the defects of distribution, irregularity, etc. over the entire substrate, a luminous quantity from the entire substrate is measured by a photoluminescence method.
The luminous efficiency evaluation method using the test diodes is capable of evaluating the luminous efficiency of the part of the substrate from which the test diodes are formed, but is not sufficient to evaluate the entire substrate. It is certain that there exists defects of distribution, irregularity, etc. in one substrate. However, this method cannot provide such information.
As for the method of measuring the luminous quantity from the entire substrate by the photoluminescence method in order to determine the defects of distribution, irregularity, etc. over the entire substrate, there is no available method which can present data on the luminous efficiency of the actual products.